Engine systems may be configured with exhaust gas recirculation (EGR) systems wherein at least a portion of the exhaust gas is recirculated to the engine intake. Such EGR systems my enable reduction in exhaust emissions while also increasing fuel economy.
Various sensors may be included in the engine system to estimate the EGR flow and control an amount of EGR delivered to the engine intake. One example of such an EGR system is illustrated by Tonetti et al. in U.S. Pat. No. 7,267,117. Herein, an oxygen sensor is included in the engine air intake, and based on the output of the oxygen sensor, a controller is configured to adjust the position of an EGR valve to thereby provide a desired amount of EGR.
EGR systems must precisely control the flow of re-circulated exhaust. For example, too much EGR flow may retard engine performance and cause a hesitation on acceleration. On the other hand, too little EGR flow may reduce the ability to decrease heat losses to coolant by lowering temperatures of combusted gases, reduce the ability to improve knock tolerance by diluting and cooling end gases, and reduce the ability to decrease/eliminate enrichment requirements by lowering exhaust gas temperatures, for example.
An EGR valve may be included in an EGR system to control EGR mass flow in order to ensure a desired EGR fraction in the intake manifold. The main function of the EGR valve is to control the amount of the returned burnt exhaust gas into the intake manifold area of an internal combustion engine. In some approaches, the EGR valve may be adjusted based on a desired EGR mass flow rate and a measured total EGR mass at an air intake system (AIS) of the engine.
The inventors herein have recognized potential issues with such EGR control system approaches. For example, the inventors herein have recognized that accurate control of an electric EGR valve requires accurate exhaust backpressure estimates, but this value can have various sources of error which degrade EGR flow estimation. For example, errors in estimating exhaust pressure differences between the output of a turbine and an EGR valve or errors in estimating a pressure drop across the EGR valve may lead to potential errors in the EGR valve position commanded by a controller. Such estimation errors could lead to either too much or too little EGR valve lift and consequently delivery of an incorrect amount of EGR to the engine intake based on engine operating conditions. Delivery of an incorrect amount of EGR to the engine intake may potentially cause fuel economy and tailpipe emissions degradations, e.g., due to engine misfire because of excessive EGR being delivered.
Thus, in one example approach, the above issues may be at least partly addressed by a method of operating an engine including an EGR passage and an oxygen sensor comprising adjusting valve position based on desired EGR flow and estimated EGR flow, where the estimated flow is based on estimated exhaust backpressure, and the estimated exhaust backpressure is updated based on errors between actual and desired intake oxygen concentration.
In this way, errors in exhaust back pressure determination based on a desired EGR rate and an actual rate determined via an intake air oxygen sensor may be used to adapt pressure estimations across the EGR valve so that a target EGR flow rate may be accurately achieved. Further, errors between actual and desired intake oxygen concentrations may be used to adaptively update exhaust back pressure estimations to control the EGR valve to meet target EGR dilutions in the engine. By determining errors in exhaust backpressure estimates and adapting EGR flow estimations based on these errors, increased accuracy in EGR valve control may be achieved thereby potentially increasing engine performance, increasing fuel economy, and reducing engine emissions.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.